1. Field of the Invention
The present invention relates to a display system used with a sequence controller for automatically operating a controlled-objective according to a control sequence stored in a memory unit. The invention relates more particularly to a display system capable of displaying a necessary sequence block obtained from the control sequence stored in the memory unit.
2. Description of the Prior Art
The sequence controller which automatically controls a controlled-objective such as a machine tool in a predetermined sequence usually comprises a memory unit in which a control sequence is stored. The control sequence includes a large number of instructions. It is often necessary to search the desired sequence block which is made up of several instructions and to display it. This need arises when, for example, a certain specific block of a control sequence is desired to be partially checked or modified. To do this, the content of the block to be modified must be checked and the desired sequence block must be obtained and displayed. In practice, however, it is not easy to obtain only the desired sequence block from the control sequence stored in the memory unit. In the memory unit, instructions are stored at addresses in a regular order, and several instructions which constitute a sequence block to be searched are stored in several memory cells with a series of memory address numbers. In particular, it is difficult to know the memory address number of the first instruction and the memory address number of the last instruction of the sequence block to be reviewed.
One solution to this problem is the use of a table setting forth instructions and their memory cells with memory address numbers on which the desired sequence block can be found. This table seems convenient, but it takes time to prepare and a considerable amount of effort is needed to find the desired sequence block from the table. Another solution is the display of the whole control sequence from which the desired sequence block may be found. This, however, also requires a large expenditure of time and for that reason is impractical.